The present invention relates to apparatus for separating and delivering flat articles of random thickness from a stack of such articles. More particularly, the invention relates to apparatus for separating such articles, one at a time from a stack, and delivering each separated article to a transfer device upon the occurrence of a command for individual article delivery.
In automated systems for handling flat articles of random size and thickness, such as mail pieces, two categories of article separator/feeders have been used traditionally, namely, fixed pitch and constant gap. In a constant gap feeding system, the feeder is designed to separate and feed a new article within a specific time frame after a previous article has been fed. This fixed time gap allows the maximum density of articles to be fed into a non-compartmented transport system within the capabilities of a particular feeder. The number of articles fed per unit time is inversely proportional to the average article length.
In transport systems which operate with compartments, such as conveyed trays or bins to receive separated articles, it is necessary to feed articles at a fixed pitch rate so that the articles will register with the respective compartments pre-designated to receive them. If a feeder is unable to deliver an article within an increment of time during which a compartment is available at the point of article delivery, a jam will occur and the transport system must be shut down to avoid damage to the article or the transport equipment.
Transport systems are further divided into two groups differentiated by the separation means employed to isolate and deliver individual articles from a stack, that is, direct friction or vacuum pickup. Each system has advantages and disadvantages and both types are common in flat article handling.
Both methods have proven to be unreliable where the article mix is high or where the interval between a feed command and article delivery is short. This latter condition is particularly evident in fixed pitch transport systems where timing of article feed is critical to jam-free operation. As a result, current fixed pitch systems are limited to very coarse pitch or very low speed.
Friction separators include systems where a prepared batch of flat articles, such as mail pieces, is presented to the separator as a stack, and a set of rollers or belts pick off, by friction, the foremost or first article while the article stack itself is held under pressure against the pick-off rollers or belts. However, as a stack is presented to the separator, the pick-off rollers or belts will not only pick off the foremost article but will also slide a number of the succeeding articles in the stack in lumps or in a step-like manner. The slip will occur at the point of least resistance, which may be several articles away. If no inhibiting gate is provided, many articles could be fed at once into the take-away system for delivery to a transfer apparatus.
To prevent separation and delivery of multiple articles, an anti-doubler roller, belt, friction pad, vacuum brake or other device is used to allow only the first, end most article to pass from the stack to a transfer conveyor or the like. Most anti-doubler devices presently used require an outside power source, such as electricity, vacuum, or air pressure. Such devices also can be unreliable due to the mass of the active article engaging device which prevents instant rebound to an anti-doubler position. In particular, when a thick article is followed by a thin smaller article in a high speed environment, the mass of the anti-doubler device inhibits instantaneous reaction to article thickness changes.
Some presently used anti-doubling devices function by rotating in the opposite direction of the movement required, thereby adding friction and power requirements. Also such devices can cause warping of an article when the article is very thin, causing misfeed and jams. A static friction pad, if used, does not require an outside power source, but wear or contamination of the pad on only one area presented at all times results in warping or otherwise damaged articles.
Separator/feeder manufacturers typically provide various methods of adjusting their pick-off assemblies. These adjustments are used to bias the friction separators toward the most common article types within the total mix. This permits tailoring the separator/feeder to provide the maximum thruput/lowest jam rate for a given article mix. On a friction separator this is accomplished by pressure adjustments within the various elements of the pick-off assembly. Typical of these is the pressure of the available stack of articles against the friction assembly, the pressure of the pick-off means against the anti-doubling means, and the pressure of a pinch/takeaway means in relation to each of the others.
Each of the previously mentioned adjustments must be made in an iterative and time consuming manner because each adjustment has an effect on the others. Problems occur, for example, when the effects of increasing the stack pressure in an attempt to improve traction against the pick-off device are negated by increased article-to-article friction in the stack. When any of these self-cancelling situations occur the limits of that particular separator have been reached. The whole procedure is done in an attempt to cause any feeder to perform reliably on the widest article mix. The limitations to these methods become more and more pronounced as the preferred article mix is being driven wider and wider by the industry economic requirements.
The industry has not demonstrated a friction type article feeder that can separate and feed mixed articles thicker than 3/8 inch with enough accuracy to supply a fixed pitch transport machine reliably and economically.